Fuel based on vegetable oil

ABSTRACT

The invention is based on a fuel obtained from vegetable oil for the operation of diesel internal combustion engines. According to the invention, the phosphorus content is less than 0.5 mg per kg of fuel.

The invention relates to fuel according to the main subject of Patent claim 1.

Diesel combustion engines for passenger cars and in particular for trucks that can be operated purely on vegetable oil are now available. Commercially available series engines are converted for operation with vegetable oil to achieve this purpose. The engines converted in this manner are operated either with cold-pressed vegetable oils from decentralized oil mills or with so-called fully refined oils originating from interregional extraction plants.

By now, a network of about 300 decentralized oil mills has been established in Germany for the manufacture of cold-pressed vegetable oil. These oil mills process approximately 10% of the national rape oilseed production. The vegetable oil produced by these oil mills typically exhibits a phosphorus content of between 5 and 30 ppm, or between 5 and 30 mg/kg of vegetable oil when expressed as a proportion of weight. The sum of the magnesium and calcium content is typically between 10 and 30 ppm.

The fully refined oil mentioned above is a vegetable oil that has typically been extracted from ground up fruit using hexane. The interim product occurring during the extraction is filtered, degummed and bleached. The final product has a phosphorus content of less than 5 ppm. Good fully refined oils have a phosphorus content of between 1 and 3 ppm and a combined calcium-magnesium value of between 1 and 3 ppm as well. Because the so-called fully refined oils are used mostly in the food industry, there are no regulations with regard to maximum values for phosphorus, calcium and magnesium.

Analyses for specifying phosphorus, calcium and magnesium contents of vegetable oils used as a fuel have by now led to a pre-standard of the Deutsches Institut für Normung [German Institute for Standards]. This DIN pre-standard DINV 51605 specifies the maximum content of these three substances in a fuel made of vegetable oil as follows:

-   -   Phosphorus: 12 ppm     -   Calcium+Magnesium: 20 ppm.

When operating engines using fuel according to this pre-standard, it became apparent that unexplainable incrustations often occur on the pistons, deposit themselves on the valve discs or the glow plugs, or block the catalytic converter in the exhaust, or plug up the soot filter. The exact operating conditions under which these deposits occur have thus far not been clarified conclusively.

The same phenomena occur with engines that are operated using rape methyl ester, the so-called biodiesel. Biodiesel is produced pursuant to the DIN standard DIN EN14214. This standard specifies the following maximum phosphorus, calcium and magnesium values:

-   -   Phosphorus: 10 mg/kg     -   Calcium+Magnesium: 5 mg/kg

To the extent that fully refined oils are manufactured by extraction plants not only for the food industry but also as fuel, the values for phosphorus, calcium and magnesium are steadily approaching the higher values according to the DIN pre-standard for vegetable oil as a fuel. This means that the phosphorus, calcium and magnesium content increases in instances when the fully refined oil is used as a fuel as opposed to its use in the food industry. This also leads to a cost advantage when the extraction rate is increased for fuel production or when purification efforts are decreased.

The present invention has the underlying objective of providing a fuel obtained from vegetable oils that causes no or only very small deposits under any occurring operating conditions. According to the invention, this objective is achieved by a fuel obtained from vegetable oil according to the features of claim 1.

Contrary to the trend-setting analyses of the standardization committee that approved the DIN pre-standard for vegetable oil as a fuel, and contrary to the already applicable DIN Standard DIN EN 14214, it surprisingly became apparent that the phosphorus content of the fuel plays a decisive role in the formation of incrustations and deposits. This was also misunderstood by the extraction plants that moved away from the relatively low phosphorus contents in fully refined oils for the food industry and increasingly moved toward the values for the DIN pre-standard. With a phosphorus content of less than 0.5 mg per kg of fuel (0.5 ppm) according to the invention, the incrustations and deposits are reduced for all occurring operating conditions to the extent that the reliable operation of the engine is no longer endangered.

Surprisingly, it likewise became apparent that the calcium content of the fuel obtained from vegetable oil is significantly responsible for the formation of incrustations and deposits under certain operating conditions of the engine. When a calcium content of less than 0.5 ppm and a phosphorus content of less than 0.5 ppm was maintained at the same time, almost no incrustations and deposits were apparent. Even the soot filter of a stationary engine showed only insignificant deposits after 500 operating hours.

According to newest analyses, magnesium also causes a significant formation of incrustations and coatings. If as per the invention the magnesium content is reduced to 0.5 ppm in fuel obtained from vegetable oil, this causation can be contained considerably.

Even better values are obtained when the fuel has a phosphorus content of less than 0.3 ppm. However, a reduction in the phosphorus content should be accompanied by a simultaneous reduction in the calcium and magnesium contents. Combined, these two substances should be at no more than 0.75 ppm in a preferred fuel.

Meanwhile, it was possible to verify that the required maximum values can be achieved even by decentralized cold press systems and that this does not cause a significant price increase for the produced fuel. In a collecting and mixing vessel, bentonite is mixed directly into the warm oil loaded with trub and dripping from the press screw via the drainage bars. This mixture is purified in a conventional manner using a chamber filter. The following values were achieved with these trial pressings:

Batch P Ca Mg Bentonite P Ca Mg 1 6.56 ppm 9.37 ppm 1.5 ppm 1% <0.3 ppm 1.24 ppm <0.25 ppm 2 6.89 ppm 8.13 ppm 1.6 ppm 1% <0.3 ppm 1.19 ppm <0.25 ppm 3 6.89 ppm 8.13 ppm 1.6 ppm 3% <0.3 ppm <0.5 ppm <0.25 ppm 4 46.7 ppm 36.2 ppm 13.8 ppm  2% <0.3 ppm <0.5 ppm <0.25 ppm

Columns 2-4 include the phosphorus, calcium and magnesium contents, respectively, in the pressed vegetable oil in the collecting and mixing vessel. The information in column 5 refers to the addition of bentonite to the vegetable oil in percent by weight. The information in columns 6-8 reflects the phosphorus, calcium and magnesium contents, respectively, of the treated vegetable oil downstream of the chamber filter. Some of the information in columns 6-8 indicates that the detection limits of the commissioned laboratory had been reached. Thus, it cannot be excluded that the actual values may be significantly below these values.

It has also been discovered that potassium contributes to the deposits. The potassium content differs significantly in different varieties of vegetable oil. It is, therefore, advantageous to establish a limit value for potassium as well. It was found that no negative influences exist with regard to the formation of deposits when a limit value of 1 ppm is maintained.

Below, it shall be illustrated how the fuel according to the invention may be produced. Pressing and purifying of vegetable oil in a decentralized cold press system shall serve as an example. FIG. 1 shows a block diagram of a method for producing the fuel from vegetable oil seeds according to the invention.

The press 1 is typically designed as a screw press. A screw rotates within a cage that is formed of drainage bars that run parallel to the screw axis. As a rule, the oleaginous fruits do not require prior grinding because they are broken in the screw press to the extent that the oil can be pressed out.

The precise adjustment of the distance between the drainage bars is responsible for the content on trub substances in the drained vegetable oil. However, this content is not only a result of the design conditions of the press 1 but also of the water content of the oleaginous fruits. In any case, it is the objective to set the draining vegetable oil to a certain content of trub substances.

The vegetable oil runs into a collecting and mixing vessel 2. There, it is stirred by a mixing paddle (not shown). Simultaneously, this prevents sedimentation of the trub substances in the collecting and mixing vessel 2. The vegetable oil heats up during pressing and exhibits a temperature between 40 and 70° C. in the collecting and mixing vessel depending on the degree of pressing. At this temperature, the vegetable oil is of low viscosity and layers that would prevent a uniform distribution of the trub substances do not occur.

Clay material such as acid-activated bentonite is added via the metering device 4. The addition is governed by the content of trub substances in the collected vegetable oil. In the same manner, the content of phosphorus, calcium and magnesium after pressing needs to be considered. It is understood that heavily pressed oil exhibits a higher content of these substances than gently pressed oil.

The pump 8 extracts the oil from the collecting and mixing vessel 2 and presses it through the filter 3. The pressure present upstream of the filter 3 is determined using a pressure sensor 10 and is transmitted to the control device 5. The oil flowing from the filter 3 is checked using the optical sensor 9. This optical sensor 9 determines the content of trub substances, for example, via the transparency. From the filter 3, the oil arrives at the 3-way valve 6 and from there is returned to the collecting and mixing vessel 2 or delivered to the tank 7. The 3-way valve 6 is controlled by the control device 5.

The control device 5 determines the speed of the rise in pressure upstream of the filter 3 via the pressure sensor 10. The filter cake in the filter 3 builds up in proportion to the pressure increase. Thus, the rise in pressure is also a measure for the trub substance content in the oil in the collecting and mixing vessel 2. The metering device 4 is controlled in relation to the rise in pressure and a computed amount of clay material is added.

The control device 5 checks the pressure upstream of the filter 3 continuously via the pressure sensor 10. As long as the pressure sensor 10 determines a value that is below a predetermined threshold value, the 3-way valve 6 is controlled such that the oil returns to the collecting and mixing vessel 2. In this manner, the oil circulates across the filter 3. The function of the circulation is to build up of a filter cake. The filter cake has the function of a high-grade filter and must, therefore, reach a thickness that ensures a sufficient filtration of the vegetable oil.

Only when the threshold value is exceeded at the pressure sensor 10, the transparency of the oil downstream of the filter 3 will be checked as well using the optical sensor 9. A threshold level for the transparency is stored in the control device 5 as well. If the transparency of the passing oil is greater than the stored threshold value, the control device 5 will toggle the 3-way valve 6. From this moment, oil is pumped into the tank 7.

Because the filter cake continues to build up, the pressure upstream of the filter 3 also continues to increase. Thus, a maximum value is stored in the control device 5. The filter 3 must be cleaned when this maximum value is reached. To accomplish this, the pump 8 is typically stopped and the filter 3 is dried using air. The dried filter cake is loosened by manual shaking or by automatic vibrations and is removed downwards. The process can then restart. Typically, the collecting and mixing vessel 2 is designed such that the draining oil can be stored temporarily during the cleaning period allowing the press 1 to continue operation even during the cleaning break.

A second filter parallel to the first filter can be provided as an alternative. Vegetable oil is fed alternating to the two filters such that cleaning can be carried out continuously. During the time when one of the filters is cleaned and a new filter cake builds up, the filtration of the vegetable oil is maintained by the parallel filter.

REFERENCE CHARACTER LIST

-   1 Press -   2 Collecting and mixing vessel -   3 Filter -   4 Metering device -   5 Control device -   6 3-way valve -   7 Tank -   8 Pump -   9 Optical sensor -   10 Pressure sensor 

1. A fuel obtained from vegetable oil for operating diesel combustion engines the improvement wherein the phosphorus content is less than 0.5 mg per kg of fuel.
 2. A fuel as set forth in claim 1, wherein the calcium content is less than 0.5 mg per kg of fuel.
 3. A fuel as set forth in claim 1, wherein the magnesium content is less than 0.5 mg per kg of fuel.
 4. A fuel as set forth in claim 1, wherein the phosphorus content is less than 0.3 mg per kg of fuel.
 5. A fuel as set forth in claim 3, wherein the combined calcium and magnesium content is less than 0.75 mg per kg of fuel.
 6. A fuel as set forth in claim 1, wherein the potassium content is less than 1 mg per kg of fuel.
 7. A fuel obtained from vegetable oil for operating diesel combustion engines, the improvement wherein the sum of the phosphorus content and the calcium content is less than 1.5 mg per kg of fuel.
 8. A fuel as set forth in claim 7, wherein the sum is equal to or less than 1.0 mg per kg of fuel. 